Dual band antenna transformer



NOV. 1, 1938. J V 2,135,234

DUAL BAND ANTENNA TRANSFORMER Filed Oct. 10, 1955 1500 2000 2500 Jose5500 I FREQUENCY K/LOCYCLES 33 43 fia a 9'- 4 I Patented Nov. 1, 19382,135,234

UNITED STATES PATENT OFFICE DUAL BAND ANTENNA TRANSFORIVIER John V.Fill, Chicago, Ill., assignor to Ferrocart Corporation of America, NewYork, N. Y., a corporation of Delaware Application October 10, 1935,Serial No. 44,444

8 Claims. (01. 250-20) This invention relates to radio receivers and uumtube T is illustrated as a simple triode ammore particularly to antennatransformers formplifier whose control grid and cathode serve as ingpart of radio receivers designed for operathe input terminals of thereceiver. Other types tion on a plurality of frequency bands. of vacuumtubes may be used in this input stage The commercial development ofiron-cored which works into other amplifier and detector radioinductances has resulted in reductions in stages which may be of anyappropriate design the size and improvements in the performance of andare indicated schematically by the block AD radio receivers. Inductancesand transformers which precedes the reproducer R. of high efficiencyhave been produced for use in The described receiver circuits will berecogthe broadcast and higher frequency ranges, but nized as thosecustomarily employed in dual range 10 the same high efficiency was notobtained in receivers operating on the broadcast and police the case ofiron-cored antenna transformers of bands. As usually constructed, thesecondary the type having a tapped grid coil, one section of windings L1and L2 have been a continuous solethe coil being shorted out during thereception noidal winding and, in adapting the iron-cored of signals inthe higher frequency band. inductances to this dual range receiver, itwas 15 An object of this invention is to provide a pr pose to u a sin ppniv l W ndradio receiver for operation over a plurality of s 011 a CoreConsisting 0f fi e y d v d a frequency ranges, the receiver including anironinsulated iron part c This arrangement had cored antenna transformerof such design that a go efiieiehcy Over the lower qu y range theshorting out of a section of the grid coil or in which the entire coilwas used, but had a low 20 transformer secondary is not accompanied byefficiency Wh n one i n w s shorted r a loss in efficiency. A furtherobject is to proception in the higher ranges. vide an antennatransformer for a double range In accordance with this invention, thesections radio receiver, the transformer including an air L1 and L2 arearranged, as shown in at core primary and a pair of spaced secondary ppe of 81 COmmOh Cy r a e M 25 sections on a common magnetic core, thesecof fi ly divided magnetic material, and the p ondary section which isto be shorted out being y W ding L3 is coaxial with the secondaries moreremote from the primary than is the secand spaced therefrom at the sideadjacent the ondary section that is tuned over the higher higherfrequency range 2- All Of the Coils frequency range. are of theuniversal winding type, and the an- 30 These and other objects andadvantages f the tennacoil L3 does not have a magnetic core. Theinvention will be apparent from th follgwing relative arrangement of thecoil terminals in the specifications when taken with the accompanyradiocircuit is indicated by the reference numering drawing, in which: als ofFigs. 1 and 2. The inner terminal I of the Fig. 1 is a fragmentarycircuit diagram of antenna coil L3 is grounded, while the outer ter- 35double range radio receiver; minal 2 is connected to the antenna. Theouter Fig. 2 is a side elevation, partly in section, of terminal 3 f thigh frequency du t L2 an antenna transformer embodying the present isConnected to the Control grid of tube t invention; and junction 4 of theinner terminal of coil L2 and Fig. 3 is a curve sheet illustrating th lti the outer terminal of coil L1 is connected to the 40 merits of thenovel antenna transformer and one Contact of Switch 3, and the innerterminal 5 of having a s ngle tapped secondary coil. coil L1 isconnected to the AVG lead.

In the drawing, the reference character Aiden- In the particularphysical s y Shown in tifies an, antenna which is coupled to the vacuum2, the Core M is fitted Within the Outer d 475 tube T in the input stageof the double range Of an insulating tubes Which y he of p p radioreceiver through a transformer having secand the Coil L1 is p t y a inedwith the ondary sections L1, L2 and a primary winding L3. Outer end ofthe Core- Coil L2 is eppleXimetely The secondary is tuned by a condenserC and a alihed With the pp end of the Core, and the switch S is providedfor shorting out the sec- Primary 0011 L3 is Spaced below the 0011 2 t0ondary section L1 when the receiver is to be op- P v the desiredcellplihgerated over the higher frequency range. The In one particularembodiment of the invengrid will usually be returned, for directcurrent, tion, the coils L1 and L2 had a combined inductto an automaticgain control system, as indicated ance of 220 microhenries, theinductance of coil by the lead AVC, and for radio frequencies is L2 was40 microhenries, and the inductance of grounded through the condenserC1. The vaccoil Ls was 2 millihenries. The core and the 5 several coilsmay be individually adjusted along the tube 6 to bring the self andmutual inductance of the secondaries to any desired values, and theparts may then be fixed in place by wax 7. A dowel 8 is fixed in thelower end of tube 6 and carries a bolt 9 for attaching the transformerassembly to a chassis.

The advantages of the invention will be apparent from a comparison ofthe curves of Fig. 3. Curve l0 illustrates the relationship between thefactor Q, equal to and frequency over a range of from about 1500 to 3500kilccycles, for an iron-cord antenna transformer having a tappedsecondary in the form of a single universal winding. The entire coil hada good Q value When used at the lower frequency range but the Q valuefell to values of from about 50 to when one section was shorted out bythe switch S, Fig. 1. A transformer such as shown in Fig. 2 had a Qvalue as indicated by curve H. The Q value is a fair measure of themerit of a radio frequency element and it will be noted that thisinvention provides a means for materially increasing the eiiiciency ofoperation in the higher frequency range of a dual range receiver.

It is to be understood that the invention is not limited to theparticular frequency ranges or to the values herein given by way ofexample. Various changes which may be made by those familiar with thisart in adapting the principles of this invention to the same or otherdesign requirements fall within the spirit of my invention as set forthin the following claims.

I claim:

1. In a radio receiver adapted to be operated over a pair of frequencyranges, an antenna transformer comprising an air core antenna coil, 2.pair of serially connected secondary coils spaced at different distancesfrom said antenna coil, 2. core of magnetic material in substantiallyfixed position axially spaced from said antenna coil and in the field ofsaid secondary coils, and switch means for short circuiting thesecondary coil more remote from said antenna coil.

2. A dual range radio receiver of the type including an antennatransformer having a secondary winding in two sections, means connectingsaid secondary winding across the input terminals of the first vacuumtube stage, and switch means for shorting one section of said secondarywinding for operation at the higher frequency range, characterized bythe fact that said secondary winding comprises two space woundmultilayer coils spaced apart along and in substantially fixed positionwith respect to a single magnetic core.

3. In a dual range radio receiver, the combination with an antenna andan input stage including a multiple electrode vacuum tube, of an antennatransformer comprising three spaced coils in axial alinement, astationary core of magnetic material within two of said coils, saidthird coil being a single continuous winding, means for connecting saidthird coil between antenna and ground, means serially connecting thefirst two coils between two electrodes of said vacuum tube, and switchmeans for short circuiting one of said first two coils.

4. The invention as claimed in claim 3, wherein said switch means shortcircuits that one of the first two coils which is the further removedfrom the third coil.

5. In a double range radio receiver, an antenna transformer comprisingan insulating tube, means at one end of said tube for securing the sameto a support, a stationary core of magnetic material fixed at theopposite end of said tube, a pair of space wound secondary coils on saidtube adjacent said core, and an air core primary coil on said tube andspaced from said core and secondary coils.

6. The invention as set forth in claim 5, Wherein the inner terminal ofthe secondary oil adjacent said primary coil is connected to the outerterminal of the other secondary coil.

'7. In a radio receiver, an antenna transformer comprising a paperinsulating tube, means at one end of said tube for securing the same toa support, a core of magnetic material fixed within said tube and spacedfrom the supported end thereof, a pair of space wound coils mounted onsaid tube about said core and spaced from each other, said coils beingserially connected, 4;

a tuning condenser connected across said coils, and means coupling anantenna to said coils.

8. A radio receiver as claimed in claim 7, wherein said antenna couplingmeans comprises an air core universally wound coil mounted on said tube.

JOHN V. FILL.

